Process of producing ammonia from alkali ferrocyanid.



LS1-INCH;

Paocgss es Peenucme AMMONIA FROM ALKAU FEaRocvANm. a m r AFFLIQATlON FILED 1ULY23, 1918. v

Patented Feb. 2o, 1919.

2 SHEETS-SHEET x.

Patened Feb. 25, IQISL APPLICATION FILED JULY 23. ISIS.

TTR/VEK lilas,

r oserei-i;

LEON S. FINCH, OF DOVER, NEW JERSEY, ASSGNOR TO HERCULES POWDER COMPANY, 0E WLMINGTON, DELAWARE, A CORPORATON OF DELAWARE.

PROCESS OF PRODUCING AMMONIA FROM ALKALI FERROCYANID.

Application filed July 23, 1918.

To IU lli/wm 'it may conoci/"n:

Be it vknown that l, LEON S. FINCK, a citizen ot the United States, residing at Dover, county ot' hf'lorri's, and State of New Jersey, have invent-ed a new and uset'ul lmprovement in Processes ot' Producing Ammonia from Alkali Ferrocyanid, of which the following` is a full, clear, and exact description,reference being had to the accompanying' drawings, which form a part ot' this specification.

This invention relates to the hydrolysis of alkali metal ferro-cyanids into ammonia and other compounds. The invention is applicable to the production of ammonia from cyanid produced by passing nitrogen over a mixture of an alkali or alkaline earth metal compound (such as sodium carbonate), carbon and finely divided iron, thereby formingv a cyanid of the alkali metal used. This method is old and well known and has been Successfully practised and even commercially used in Europe. The process, however, has not gone into general use, largely because of the practical diliiculties encountered in the attempt to secure a good yield of ammonia from the cyanid.

lt is well known that when cyanids are subjected to the action ofsteam at a relatively high temperature ammonia is formed. 'With sodium cyanid, the equation would be:

(l) NaCN-l-2H20:llCO,a-NH

lVhere, however, the product ot the cyanid-t'orming reaction contains carbon, iron, sodium terro-cyanid, sodium hydrate and sodium carbonate, the simple. method of distilling with steam, or the other obvious expedient ot adding water and heating under pressure in an autoclave, gives comparatively poor results, even when the insoluble materials (carbon and iron) are entirely removed.

There carbon alone is used, or where, in addition to carbon, iron is employed as a catalyzer in relatively small proportions, or where, due to some particular method of procedure, no alkali metal ferro-cyanid is formed, or comparatively little alkali metal ferro-cyanid is formed, it is found possible to hydrolyze the cyanid mixture to ammonia, even though the same contains other impurities,bv;mxing the cyanid mixture with Specification of Letters Patent.

Patented Feb. 25, Mirti..

Serial No. 246,360.

after the distilling operation has proceeded for some little time. This process forms the subject-matter of an application iiled of even date herewith, Serial No. 245,279.

Vher'e, liowever, the aqueous solution passing to the still contains a considerable proportion ot ferro-cyanid, it is found impossible to hyd rolyze efiiciently the jerro-cyanid under the low pressure conditions well adapted to the hydrolysis of the cyanid. Only the cyanid and a very small amount of sodium terro-cyanid will 'be converted into ammonia and the yield of ammonia from the mixed eyanids Will` be proportionately reduced. The presence of a large proportion of terro-cyanid may be due, partially, to the large proportion of iron used in the cyanid process. The use of large percentage ot iron is generally, but erroneously, supposed to be necessary; by far the highest yields of alkali metal cyanid being produced when the proportion of iron is about ten or twelve per cent. The use of some iron, however, is desirable, because its presence makes it possible to conduct the cyanidforming process at a temperature much lower than is possible where carbon alone is used. Under proper conditions of operation, ferro-cyanid will be produced in very small quantity.

However, although the mixture may contain little terro-cyanid, upon the addition of water, the conversion of cyanid inito ferrocyanid proceeds, and if the mixing operation or the filtration operation is a relatively slow one, or if the solution is allowed to stand, ferro-cyanid will form in considerable quantities and, as before sta-ted, its hydrolysis to ammonia will be almost impossible under conditions adapted to the hydrolysis of the cyanid. v

Where, due to anyT of the aforementioned causes, the aqueous solution contains a considerable proportion of ferro-Cyanid, it ma be advisable, rather than to attempt to simu taneously convert to ammonia both the cyanid and ferro-cyanid, to convert all-or most of the cyani d to ferro-cyanid and then modify the distilling process to adapt it to the treatment of ferro-cyanidll/ly invention comprises such a modification, and it is, ofl course, adapted to the treatment of ferro-cyanid however ift may be produced. My invention comprises' not only a process for hydrolyzing ferrdeyanid to ammonia, but also contemplates" thnwrsion of mixed cyanid and ferro-cyanid to ferrofcyanid preparatory to its distillation, and even contemplates the preliminary conversion of cyanid to ferrocyanid where no ferro-cyanid is initially present. The present process exhibits featurcs common to the process for treating cyanid9 which features are claimed in the application hereinbefore mentioned, the subject-matter claimed herein being such modification of said vprocess as adapts it to the production of ferro-cyanid and its hydrolysis into ammonia.

While the process is not dependent for its execution upon any particular' apparatus, it is preferred to carry out the process in an apparatus lconstructed sulostantiallyy in accordance with the accompanying drawings, wherein Figures l and 2 'are diagrammatic views showing two parts of the apparatus.'

lt may be assumed that the cyanized material contains sodium cyanid, sodium ferrocyanid, sodium hydrate, small quantities of sodium carbonate and sodium sulfate, and carbon and iron. The material is cooled in an atmosphere of nitrogen, powdered, and

. one part of powdered material isv agitated with one to three parts of water in a suitable tank, sufficient time beingr allowed for the Sodium cyanid to react with the iron to form sodium ferro-cyanid, according to the fol lowing1 equa-tion: l

(2) NaCN-l-Fe-l-QHZ: l

Na4Fe (CN) .,-l-QNaOH-i-Hz 'time of reaction may vary. from one to twenty-four hours.-

From the mixing tank, a pipe e leads to a filter f. This lter may be of thefrotary continuous type shown, which filters rapidly and continuously, or it may be a iilter of any eiicient type. lt need not be rapid or continuous in its action. From the filter, the

ferro-cyanid solution may pass direct to the still j (see Fig. 2); but it is preferred to convey it through a pipe g to a stdrage tank tained' by the filtration may contain only a.Y v

trace of sodium cyanid, but it isnot neces sary to the Asuccessful execution of the process that the conversion-to sodium ferro-cyanid should be complete. A considerable quantity of sodium cyanid may be present in the solution without preventing the suc-' cessful execution of the distilling process.

rihe still is approximatelyhalf-filled. Within the still, preferably the lower part, are steam coils 7c, which at one end are connected with steam inlet pipes m and at the other end with steam traps n. There is also a steam pipe o entering` the interior ofthe still, which provides an eilic-ient way to rapidly heat the contents of the still when the solution become; too concentrated. The pipe should extend beneath the surface of the cyanid solution.

At the top of the still is a pressure relief valve p which controls the passage of the distillate to a trap tank r.. The trap r is also connected with a reflux' condenser s. which may be air-cooled, but which is -preferably Water-cooled. The condenser s is connected with an ordinary water-cooled condenser t, which is tipped downward so as to drain into a neutralizingtub (not shown)- Steam at about li@ pounds pressure is preferred. f the solution in the still is too concentrated, it is advisable to admit steam direct into the' still, thereby more rapidly heating the contents,I and at the same time reducing the concentration. When the solutiton is of the concentration desired, steam should be admitted solely to the' steam coils.

The relief valve is set to open at a pres- EID sure not less than pounds per square inch, and it is preferred to set it so that a much higher pressure will be maintained.l At. a pressure of less than 80' pounds the yield will not be eflicient. The preferable pressure is nearer 150 pounds to the square inch. The higlier pressure is preferred be Y cause the higher: the pressure the more rapid means of the relief valve, is of irnportance,A

and seemsto necessary in order that the process shall operate efficiently and without mechanical trouble.

rilhe distillate (steam and ammonia) es,-v

caping' at the relief valve passes to the trap tank 7' and thence to the reflux (preferably water-cooled) .condenser 8. Nearly all the Leeaaea moisture which escapes with the ammonia is condensed in the condenser s and returns to 'the trap tank. The ammonia which passes on through the condenser s is cooled by passing throuffh the water-cooled con denser z-, which drains into the neutralizing tub above inentioner.

at the start of the run gaseous ammonia produced and at the end oit the run aqueous ammonia. lt is not especially sought, however, to produce gaseous anunonia, but strong' ammonia. solution, so that the subsequent neutralized liquor will requirey as little evaponallion as possible. Y Hence, all distillate which collects in condenser 25 is allowed to pass into the neutralizing tub.

The ammonia which passes through condenser t is stronger than that which is con.- densed by the reflux condenser s. The strength of the ammonia which passes into the neutralizing tub depends upon the relative sizes of the two condensers and the manner in which the condenser 8 is cooled. A relatively large reflux condenser will condense relatively more moisture and the arninonia passing' through condenser t will be relatively stronger, provided other operations are the same.

The aqueous ammonia which collects in the trap tank fr is much weaker than that which passes into the neutralizing tub. This weak distillate may be utilized as such, or it may be pumped back into the hydrolyzing still and redistilled, giving a strong; ammonia. The pumping back into the still of this weak aqueous ammonia is also advantageous in that the liquor in the still is prevented filoni reachingf too high a con centration. Y

The sludge left in the still may be drawn oli through a valve gate 'u and is used in the manufacture of more sodium ferro-cya-l nid or for theproduction ot' formate comu pounds.

By the process described, from l0 to 8G per cent. of the theoretical ammonia distils ofi` during the first hour. At the end of less than six, hours practically 1'00 per cent. of the theoretical ammonia is distilled of?. These results are attained with a full sized apparatus operating on a commercial scale. The rate at which the ammonia distils oil' will depend upon the size and construction of the apparatus, the temperature and pressure, and the concentration of the liquor in the tank.

'The decomposition probably tal-:es place according to the following1 equation:

From this reaction it will be seen that in order to get a complete hydrolysis of the sodium ferro-cyanid into ammonia, it will be necessary to have enough sodium hydrate ate.

present to satisfy the reaction. This will probably automatically be taken care of due to the tact. that in the preparati )n oi cyanized material trom sodium carbonate, seine or" the sodium carbonate which is not coin.- pletely fixed to sodium cyanid will be reduced to sculiurrL oXid. The sodium oxid on i'iltration will then react with the water to rive the sodium hydrate which is called lfor in this reaction. lv'loreover, by referring to equation 2, it will be seen that Jfor every molecule oi sodium l'erro-cyanid formed from sodium cyanid, there are also formed two molecules of sodium liydrate. This amount of sodium hydrate is the exact theo retical amount required to satisfy' equation Hence it will probably not 'be necessary to add any hydrate, but in some cases itY 4may be advisable to do so.

While actual practice demonstrates the success ot' the process as applied to a sodium iterro-cyanid solution containing so? diam cyanid` and the impurities hereinbefore specified, it is believed that the process will operate equally well where other irnpurities are present as the result of producing the ferro-cyanid by other processes. linpurities do not apparently affect the reaction. Nor is the processi limited to a ferro-cyanid produced from sodium carbon- The ferro-cyanid may be made from other alkali or'alkaline earth metal compounds. .Generally speaking, the process is applicable to any ferro-cyanid, however produced, Whether pure or impure, it being understood that in the known processes for. producing ferro-cyanid, especially those in which an alkali metal salt, carbon and iron, are acted upon by nitrogen, the presence of impurities Correspendingto those hereinbefore mentioned, is unavoidable. One-ot the advantages of the process is that it is not essential, on the one hand, to purify the solution resultingr from leaching' the material from the furnace, nor, on the other hand, to make any addition to the leached solution.

Having now fully described my invention, what l claim and desire to protect by Letter Patent is:

1. rljhe process of producing ammonia from a solutionof alkali metal terro-cyanid which comprises'distilling oli' the ammonia by heat while maintaining the solution under a substantially constant pressure not less than 80 pounds to the square inch.

2. The process of producing ammonia I from a solution of alkali metal ferro-cyanid which comprises subjecting the solution to heat and pressure Within aconfined still and providing tor the intermittent. escape of the distillate whenever the pressure reaches a predetermined maximum, said maximum be? inghnot less than 8O pounds to the square me 3. The process of producing ammonia from solution of .si i inet/ui fcrro-c-yu-nif which comprises suine-sting the sciution 'toheat i and to a pressure not less than pounds to the square inch to distii @E ammo nia and water vapor, and condensing out Water vapor from the distillate anti retum ing it to the still.

4i. The process oi. producing ammonia from' a solution of eikaii incisi fern-cys nid which comprises distilling off ammonia and Water Vapor by heat While maintaining the solution under a pressure not less than pounds to the square inch, and subjecting the distillate to a. plurality of successive con* densations at progressiyely-decreusine tern peratures. l

5. The process of producing ammonio,

' from a solution of alkali metai crrecyenia which comprises distiliing ci? ammonia Water vapor by heat Whiie maintaining 'the solution under a pressure not less than 8G pounds to the square inch, condensing out Water andyapor from the distillate, return ing the condensed vapor to the solution, und subjecting the uncondensed distillate to further condensation.

6. The process of producing mansioni?W from alkali metal cyanici, iron and carbons which consists in adding to the mixture a liquor consisting Wholly or mainly of Water,

lmixing and agitating until a .substantici amount of cyanid, 'by reaction with the iron, is converted to erro-cyumci, removing iniii soluble material from the aqueous 1' 'is converted to terro-cyunid7 removin soiucie materiau from the aqueous ieri-roftne convo.

wiioiiy er mniniy of vente@ ammonis un @irritating untii e substuntiell di 1 1 amount ci cy ni oy reaction. *with the iron,

cyanid. soiution, and dis-tiliing ofi tirs s,

munie, by heat While maintaining the sciution vunder e substantieiiy constant pressure not less 8@ pountis to the square inch. y

The process producing ammonia *n Wirtin-e containing' @ii-mii solution or l nifi ci u-cysiiici i :ammonia by heet cncipressnrs. Y l

9.- The pocess of proucing ironi e, inixtizre containing uikci instel eyenid '1 si sii meta-i ,ferrocyanid, Winch consists in meiziug su mucous soiution of the cysniii and iferrocya-ni, adding iron to eiect conversion of more or icss ci the cyanid to errc-cya-nid, end distiiiing @E 4 the ammonia byhcat and pressurc.

in testimony of which' nveutcm hereunto set uy this 119th i um isis Y reno., at Kemfii, N. in on 

